The pressure on Franken has been growing since two more women stepped up Wednesday to accuse him of inappropriate sexual conduct. Those accusations triggered an avalanche of calls from dozens of his senate colleagues to resign.

While Thursday morning's Twitter post gives no mention as to what Franken's announcement will include, long-time political science professor Steven Smith believes it will be his resignation.

"That gives the governor 24 hours to scramble and make some new plans," Smith said.

Under Minnesota law, Governor Mark Dayton will first name an interim replacement for Franken.

Then, at the August 14, 2018 primaries, voters will elect a candidate from each party.

At the General Election on November 6, 2018, voters will select the new senator to finish the last two years of Franken's term.

Finally, in November 2020, there will be another election for a new six-year term.

Smith says Dayton's immediate appointment is very important.

"Because that person would have a leg up, be serving in the Senate. And gain a lot of free publicity," Smith said.